The invention relates to films of crosslinked fluoropolymer that serve as lubrication and/or protection coatings. The invention more particularly relates to magnetic storage media having a crosslinked fluoropolymer lubricant layer.
Advances in many technologies have created enhanced demands on materials used in the production of a variety of devices. Specifically, miniaturization has decreased tolerance levels while increasing performance requirements. Furthermore, coating technology has become extremely important since coatings can be used to alter the surface properties of the composite while maintaining desirable properties of the underlying substrate. In particular, thin coatings can serve to protect the underlying substrate from a variety of assaults.
Data storage discs for the electronic storage of information are a device of particular interest. Disc drives for data storage can use one or more data storage discs with a magnetic medium for the storage of information. The magnetic medium generally is formed by a relatively thin magnetic layer on a non-magnetic substrate. Typically, the data is stored at specific locations along concentric data tracks. The disc drive assemblies for magnetic data storage include head/gimbal assemblies aligned with the disc surface. The head/gimbal assemblies support transducers, such as magnetoresistive elements, for reading data from and/or writing data to the data tracks near the disc surface.
The read/write head generally includes an air bearing surface, which faces the disc surface. As the disc rotates, the disc drags air along the air bearing surface. As the air passes along the air bearing surface, the air pressure between the disc surface and the air bearing surface creates a hydrodynamic lifting force that causes the slider or head to deflect away from the disc surface. Prior to rotation of the disc, the slider rests on the disc surface. The hydrodynamic lift is affected by the speed of rotation of the disc, the design of the air bearing surface of the read/write head, and the preload force supplied to the head by the gimbal assembly.
Discs can include separate landing zones and data storage zones on the disc surface. Information is stored in the magnetic media within the data storage zones. The landing zones are used to support the slider when the disc is not rotating. The landing zones also provide a takeoff and landing surface for the read/write head. The landing zone portion of the disc surface preferably is not used for data storage since repeated contact with the read/write head can destroy stored data in the magnetic medium near the disc surface.
To obtain higher storage densities on the disc surface, fly heights between the read/write head and the disc surface are being reduced. Reducing the fly height improves the magnetic interaction between the head and the disc surface to allow correspondingly higher storage densities. Thus, it is important that the disc surface is sufficiently smooth for a particular fly height to reduce contacts between the read/write head and the disc surface. Contact between the read/write head and the disc surface can result in data loss and damage to the disc and/or the head.
Furthermore, intermittent contact between the head and the disc surface causes wear of the disc surface. To protect the disc surface from wear and corrosion, overcoats can be placed on the disc surface over the magnetic medium. Preferred overcoats reduce wear and friction while maintaining proper hydrodynamic interaction between the head and the disc surface during rotation and during take-off and landing.
Carbon coatings have been used to form protective layers on magnetic substrates. The coating, however, increases the spacing between the surface and the underlying substrate. Thus, for example in the production of magnetic discs, any performance improvement resulting from a reduction in fly height can be countered by the presence of protective coatings and the like that result in an increased distance of the magnetic medium and the disc surface.
Furthermore, lubricant layers generally are used on magnetic disc surfaces to reduce wear and to decrease friction between the disc surface and the head. Perfluoropolyethers can be used to form the lubricant layer. A variety of approaches have been explored to secure the lubricant layer to the substrate such that the lubricant layer remains on the disc surface for a longer period of time.
In a first aspect, the invention pertains to a magnetic storage medium comprising:
a first protection means for protecting a magnetic substrate, the first protection means comprising a carbon material; and
a second protection means for protecting a magnetic substrate, the second protection means comprising a crosslinked fluoropolymer.
In another aspect, the invention pertains to a material comprising a magnetic substrate, a carbon layer covering at least a portion of the substrate and a crosslinked fluoropolymer layer covering at least a portion of a surface of the carbon layer, the crosslinked polymer layer having a thickness less than about 40 angstroms and the carbon layer having a thickness of less than about 100 angstroms.
In a further aspect, the invention pertains to a material comprising a magnetic substrate, a carbon layer covering at least a portion of the substrate and a crosslinked fluoropolymer layer covering at least a portion of a surface of the carbon layer, wherein the crosslinked fluoropolymer layer has a thickness at one point on the carbon layer greater by at least about 5 angstroms than the thickness at another point on the carbon layer.
Moreover, the invention pertains to a method of forming a lubrication layer of crosslinked fluoropolymer on a carbon substrate, the method comprising irradiating selected portions of the substrate with appropriate amounts of radiation to form a crosslinked fluoropolyer layer with different thicknesses of crosslinked polymer at different locations on the substrate.